Problem:
If:
- A routine A() opened a SYS_REFCURSOR with a function B() in the SELECT list
- The function B() also opened some SYS_REFCURSORs
Then reallocation of the cursor array THD::m_statement_cursors could happen
during the execution of B(), so all sp_cursor_array_element pointers inside
sp_instr_copen_by_ref::exec_core() of routine A() became invalid.
Fix:
Chaging the data type of sp_cursor_array:
- from Dynamic_array<sp_cursor_array_element>
- to Dynamic_array<sp_cursor_array_element*>
So now only reallocations of the array of cursor pointers happen,
while sp_cursor_array_element instances always stay on their originally
allocated memory positions.
Note:
sp_cursor_array_element instances are allocated using the standart C++ "new"
and deleted using the standard C++ "delete". Using a MEM_ROOT does not
seem to be relevant here.
Adding support for the strict cursor data types:
Example 1a:
TYPE rec0_t IS RECORD (a INT, VARCHAR(10));
TYPE cur0_t IS REF CURSOR RETURN rec0_t;
Example 1b:
TYPE rec0_t IS RECORD (a t1.a%TYPE, b t1.b%TYPE);
TYPE cur0_t IS REF CURSOR RETURN rec0_t;
Example 1c:
TYPE rec0_t IS RECORD (a INT, VARCHAR(10));
r0 rec0_t;
TYPE cur0_t IS REF CURSOR RETURN r0%TYPE;
Example 1d:
TYPE rec0_t IS RECORD (a t1.a%TYPE, b t1.b%TYPE);
r0 rec0_t;
TYPE cur0_t IS REF CURSOR RETURN r0%TYPE;
Example2a:
TYPE cur0_t IS REF CURSOR RETURN t1%ROWTYPE; -- t1 is a table
Example 2b:
r0 t1%ROWTYPE;
TYPE cur0_t IS REF CURSOR RETURN r0%TYPE;
Example3a:
CURSOR cursor_sample IS SELECT a,b FROM t1;
TYPE cur0_t IS REF CURSOR RETURN cursor_sample%ROWTYPE;
Example3b:
CURSOR cursor_sample IS SELECT a,b FROM t1;
r0 cursor_sample%ROWTYPE;
TYPE cur0_t IS REF CURSOR RETURN r0%TYPE;
If a cursor variable is declared with a RETURN clause then:
1. At OPEN type the data type of the SELECT list row is compared
for compatibility with the cursor RETURN data type.
The SELECT list row must be assignable to the RETURN type row.
If case if assignability is not meet, an error is raised
Assignability means:
- The arity of the SELECT list must be equal to the arity
of the RETURN clause
- Every n-th field of the SELECT list must be assignable to the
n-th field of the RETURN Clause
2. At FETCH time, the data is fetched in two steps:
a. On the first step the data is fetched into a virtual table
with the row type described in the RETURN clause
b. On the second step the data is copied from the virtual table
to the target fetch list. Data type conversion can happen
on this step.
Change details:
Adding new methods:
- sp_cursor::check_assignability_to
- Virtual_tmp_table::check_assignability_from
- Virtual_tmp_table::sp_set_from_select_list
- Virtual_tmp_table::sp_save_in_vtable
- Virtual_tmp_table::sp_save_in_target_list
- LEX::check_ref_cursor_components
- LEX::make_sp_instr_copy_struct_for_last_context_variables
- LEX::declare_type_ref_cursor
- sp_cursor::Select_fetch_into_spvars::send_data_with_return_type
Adding new members:
- sp_instr_copen_by_ref::m_cursor_name
- Select_fetch_into_spvars::m_return_type
- Select_materialize::m_cursor_name
- Select_materialize::m_return_type
Adding new virtual methods:
- Item::resolve_spvar_cursor_rowtype
- Type_handler::Spvar_definition_resolve_type_refs
- Server_side_cursor::check_assignability_to
- Overriding Select_materialize::prepare to raise an error when the cursor
returned data type is not compatible with the RETURN clause
Making these methods virtual:
- Field::check_assignability_from
Adding new classes:
- sp_type_def_ref
- RowTypeBuffer
Adding new constructors to:
- Spvar_definition
Adding new helper methods (e.g. to reuse the code)
- Field::store_field_maybe_null
- ChanBuffer::append_ulonglong
- sp_pcontext::set_type_for_last_context_variables
Minor changes:
- Making TABLE::export_structure const
- Overriding Item_splocal::type_extra_attributes. It was forgotten in earlier changes.
Adding new error messages
- ER_CANNOT_CAST_ON_IDENT1_ASSIGNMENT_FOR_OPERATION
- ER_CANNOT_CAST_ON_IDENT2_ASSIGNMENT_FOR_OPERATION
Adding support for cursors on prepared statements.
- SQL Standard way:
DECLARE c CURSOR FOR stmt;
PREPARE stmt FROM 'SELECT ?';
OPEN c USING 1;
- Oracle-style way with SYS_REFCURSOR variables:
DECLARE
c SYS_REFCURSOR;
BEGIN
OPEN c FOR 'SELECT ?' USING 1;
This patch adds support for SYS_REFCURSOR (a weakly typed cursor)
for both sql_mode=ORACLE and sql_mode=DEFAULT.
Works as a regular stored routine variable, parameter and return value:
- can be passed as an IN parameter to stored functions and procedures
- can be passed as an INOUT and OUT parameter to stored procedures
- can be returned from a stored function
Note, strongly typed REF CURSOR will be added separately.
Note, to maintain dependencies easier, some parts of sql_class.h
and item.h were moved to new header files:
- select_results.h:
class select_result_sink
class select_result
class select_result_interceptor
- sp_cursor.h:
class sp_cursor_statistics
class sp_cursor
- sp_rcontext_handler.h
class Sp_rcontext_handler and its descendants
The implementation consists of the following parts:
- A new class sp_cursor_array deriving from Dynamic_array
- A new class Statement_rcontext which contains data shared
between sub-statements of a compound statement.
It has a member m_statement_cursors of the sp_cursor_array data type,
as well as open cursor counter. THD inherits from Statement_rcontext.
- A new data type handler Type_handler_sys_refcursor in plugins/type_cursor/
It is designed to store uint16 references -
positions of the cursor in THD::m_statement_cursors.
- Type_handler_sys_refcursor suppresses some derived numeric features.
When a SYS_REFCURSOR variable is used as an integer an error is raised.
- A new abstract class sp_instr_fetch_cursor. It's needed to share
the common code between "OPEN cur" (for static cursors) and
"OPER cur FOR stmt" (for SYS_REFCURSORs).
- New sp_instr classes:
* sp_instr_copen_by_ref - OPEN sys_ref_curor FOR stmt;
* sp_instr_cfetch_by_ref - FETCH sys_ref_cursor INTO targets;
* sp_instr_cclose_by_ref - CLOSE sys_ref_cursor;
* sp_instr_destruct_variable - to destruct SYS_REFCURSOR variables when
the execution goes out of the BEGIN..END block
where SYS_REFCURSOR variables are declared.
- New methods in LEX:
* sp_open_cursor_for_stmt - handles "OPEN sys_ref_cursor FOR stmt".
* sp_add_instr_fetch_cursor - "FETCH cur INTO targets" for both
static cursors and SYS_REFCURSORs.
* sp_close - handles "CLOSE cur" both for static cursors and SYS_REFCURSORs.
- Changes in cursor functions to handle both static cursors and SYS_REFCURSORs:
* Item_func_cursor_isopen
* Item_func_cursor_found
* Item_func_cursor_notfound
* Item_func_cursor_rowcount
- A new system variable @@max_open_cursors - to limit the number
of cursors (static and SYS_REFCURSORs) opened at the same time.
Its allowed range is [0-65536], with 50 by default.
- A new virtual method Type_handler::can_return_bool() telling
if calling item->val_bool() is allowed for Items of this data type,
or if otherwise the "Illegal parameter for operation" error should be raised
at fix_fields() time.
- New methods in Sp_rcontext_handler:
* get_cursor()
* get_cursor_by_ref()
- A new class Sp_rcontext_handler_statement to handle top level statement
wide cursors which are shared by all substatements.
- A new virtual method expr_event_handler() in classes Item and Field.
It's needed to close (and make available for a new OPEN)
unused THD::m_statement_cursors elements which do not have any references
any more. It can happen in various moments in time, e.g.
* after evaluation parameters of an SQL routine
* after assigning a cursor expression into a SYS_REFCURSOR variable
* when leaving a BEGIN..END block with SYS_REFCURSOR variables
* after setting OUT/INOUT routine actual parameters from formal
parameters.
